1. Field of the Invention
This invention relates to offshore platform structures and more particularly it concerns a novel self-contained and self-installing jack up type drilling and production rig for exploration, drilling and production of oil at offshore locations.
2. Description of the Prior Art
U.S. Pat. Nos. 2,771,747, 2,960,832, 3,001,594, 3,001,595, 3,013,396, 3,593,529, 3,716,993, 3,727,414, 3,874,180 and U.K. Pat. No. 1,446,751 all describe offshore platform structures which can be floated to a desired offshore location and raised up above the sea on self-contained legs which are lowered to the sea floor. These structures are described as being useful for a variety of applications including oil well drilling and production.
The jack up offshore structures shown in U.S. Pat. Nos. 3,001,594, 3,001,595, 3,593,529, 3,727,414, 3,874,180 and 3,999,396 are used both for drilling and for production of oil. These structures are quite complicated and expensive in that they are all made up of one portion which is used for drilling and a separate portion which is used for production. Also, the drilling portion must be moved away before the production portion can be put into operation. In most cases the structure actually involves two separate platforms each mounted on its own set of legs. In U.S. Pat. No. 3,727,414 the same legs are used to support drilling and production platforms but these platforms must be supported on the legs at different times. U.S. Pat. No. 3,999,396 shows a drilling tower mounted over a slot in the hull of an elevated offshore platform structure but no teaching is provided which would enable the same device to be used for simultaneous drilling and production operations.
Another deficiency of the prior art jack-up type offshore platform structures is that none of them are particularly concerned with the provision of a suitable conductor support in those platform structures which are to be used for oil well drilling and production operations. When drilling is to be carried out from an elevated offshore platform, a long, thin drill string, comprised of a series of connected together rods, is lowered down through an elongated tubular conductor which extends from the platform itself down through the sea and into the sea bed. Also, for production operations, one or several relatively thin conduits also extend up through the tubular conductors from the sea bed up to storage and production facilities arranged on the elevated platform. These conductors must be supported laterally, otherwise they will bend or break due to water and wind forces. The proper location or locations for this lateral support, however, will vary according to the water depth, the height of the platform above the water, the bending characteristics of the conductors, and other factors such as wind and sea conditions.
U.S. Pat. No. 3,716,993 shows in FIG. 10 a drill string supported by guides fixed to bottoms of the platform support legs. U.S. Pat. No. 3,727,414 shows a similar arrangement in FIG. 7. U.K. Pat. No. 1,446,751 shows, in FIG. 3, a drill string support extending out from the lower end of a set of upper support legs. None of these patents, however, shown any arrangement for positioning the drill string or conductor supports according to the support requirements of the drill strings or conductor supports themselves.